Set top boxes are used, for example in the context of cable television and satellite television. A set top box is arranged to receive television programs from a satellite or via a cable and to output a program which is displayed on a television screen or recorded on a video recorder. With both cable and satellite television, an input stream is received at an interface of the set top box. The input stream is generally scrambled and comprises audio and visual information about several different television programs, the information being time multiplexed together. Control information will also be included in the received input stream. Information relating to a television program selected by the user is demultiplexed by the set top box from the input stream to provide the selected program which is then output by the set top box to for example a television screen, video recorder or indeed any other type of recorder.
It has been proposed to output a copy or a modified version of the input stream via a further output interface. This copy or modified version of the input stream can be sent to another device capable of processing that stream.
In the current proposals, the copy or modified version of the input stream will include the data from the programs of interest. Thus for a packet of the input stream, only some of the bytes of the data of the packet may be related to a program of interest and be output via the further interface. The required bytes of the packet will be at the beginning of the output packet with the remaining bytes of the packet filled with an indication that those bytes are not required or are invalid bytes. The data of the bytes which are not required are discarded and are not output via the further interface.
This has the disadvantage that the relative timing of the data bytes relating to a required program in the output stream will differ from that of the input stream even if the packet start timing is the same for the input, and output streams. In other words, the relative timing of the bytes within the packet will differ.
It has been appreciated by the inventor that this may be undesirable. A processor connected to the further interface may be unable to process correctly the bytes because the relative timing of the desired bytes has changed. Additionally, the processor connected to the further interface may not be able to process the data bytes efficiently because all of the desired data bytes are bunched together instead of being distributed over the whole of the data packet.
Accordingly, it is an aim of certain embodiments of the present invention that this problem be addressed.